Process of impregnating timber



Patented Oct. 15, 1929 UNITED STATES PATENT OFFICE THEODORE W. SMITH, orINDIANAroLIs, INDIANA, ASSIGNOR TO PETER c. .REILLY,

or INDIANAPOLIS, INDIANA ruocnss 0F IMPBEGNATING TIMBER N 0 Drawing.

This invention pertains to an improved. process of impregnating fibrousmaterial, and more specifically wood fiber, with a liquid.-

More specifically, the invention pertains to the impregnation of piecesof wood, such as poles, with preservative liquids and in ,such a manneras not to injure or weaken the natural strength of the wood and at thesame time to obtain the desired distribution of the preservativethroughout the wood, or .that

- part thereof which is required to be treated.

The invention ismore particularly applicable to the treatment of thebutts of poles.

The first requirement in the process of butt-treating poles is to free,as much as possible, the wood fibers in the poles from those elementswhich interfere with the free and uniform entrance of the preservativeliquid into the cavities of the wood structure of the poles.

The principal obstructions necessary to be removed from the cavities (ifthe wood are two, air and moisture. These'I remove by the properapplication ofheat, as will be later described.

An element of obstruction to the exit-of moisture and air isintroducedinto the fibers of the poles, under ordinary practice,whenever the poles are dipped into a liquid, the temperature of which'isnot suflicient to cause the air in the cavities in the wood to expandquickly and with sufiicientforce'to prevent the absorption of anyappreciable amount of the preservative liquid, which, if absorbed,

will offer considerable interference to the ex} pulsion of air andmoisture from the wood.-.

In order to prevent initial absorption of;

the preservative liquid at the beginning of the treating process, whichwould materially interfere with the expulsion of air. and gases from thefibers of woodwhen the poles are introduced, into the liquidpreservative, the

liquid is heated so as to cause a rapid expansion of thenair and alsoinitial vaporization of moisture in the poles, thus preventingabsorption of the preservative liquid at this time.

I have found that when the preservative liquid is brought to atemperature of about that of boiling water (100 C.212 F.) andApplication filed June 21, 1927. Serial No. 200,513.

the poles are introduced slowly into the pre- 115 0. (230 F. to 240 FT)that't he desired conditions are obtained .forfavor-ab'le' e' -xpulsionof air and moisture from the-wood,

for the reason that the hot preservative fluid imparts suflicient heatto'the vapors and gases in the wood to createian expansive-"forcegreater than the upward'pressure (buoyancy )1,

of the preservative liquid'against "the butts of the poles. .On accountof "theseiunb'alanced forces, there will be an uninterrupted,

expulsion of gases from the beginning of the treating process to the.time the expansive force of the gases in the wood equals-the. buoyantforce of the preservative" liquid against the butts of the'poles which;marks the limit of the rarefication of the ,gases' at that temperature.

WhatI have found to be-the' best practice for keeping the preservativeat approximately the desired temperature from the beginning of theoperation is to place the poles in a suitable treating tank, of whichthe bottom and about four feet up the sides are fitted with steam coils,andthree or four inches above the bottom coils is placed a perforateplatform on which thebutts of thepoles rest. The preserving liquid isadmitted at the bot tom of the tank and in passing over the hot coils itis kept at uniformly high temperature around the butts of the polesalthough the preservative may become slightly cooled as it rises andcomes in contact with the cool surface ofthe poles.

v Very shortly after the preservative liquid has been added to theproper depth in the tank it is only a matter of a few minutes till allof 'the preservativ'e has reached a uniform temperature throughout. Onthe other hand the poles are plunged rapidly into the hot preservativefluid, heat is not imparted rapldly enough to the gases in-the'wood tocreate an expansive force equal to the upward pressure (buoy-- ancy) ofthe preservative liquid against the butts of the poles, there-fore someof the liquid will be forced into the cavities of the wood at thebeginning of the operation. This initial 2 5 "about212? E to. 240 F.-(or 100 c. to 115 during the process of expelling or re-, noval'of theair and moisture from the timobstruction to the liberation of the gasesis so strong that it becomes impracticable to increase the heat to atemperature sufficiently high to force this liquid out of the cavitiesof the wood, which condition hinders the proper rarefication of thevapors and gases in the wood and thus prevents a uniform distribution ofthe preservative liquid through the wood. It is this initial absorptionof the preservative liquid that has made butt-pole treating methods sounsatisfactory.

That little or no absorption may take place during the time of expellingthe air and moisture, I have found that it is necessarysto keep thetemperature of the preservative liquid in a state of slightly rising temperature from the time the poles are immersed in the liquid until, themoisture and air have been expelled. When the liquid has reached atemperature sufliciently high to ex- 7 pel the gases to, the desiredamount, the temperature canbe held at this point, without danger ofabsorption of the preservative that would interfere With the finalexpulsion of air and'moisture, the temperatures ranging from ber.;-

In order obtain the necessary space in "thewfiber ofthe' poles to eflectthe desired depth and-length of impregnation v of the wood, I immersethe poles to a greater depth than that to which the poles are to betreated or impregnated. I do this for the purpose of gaining additionalv'oided space within and throughout the pores of the wood and therebyobtain more perfect and uniform penetration throughout that part of thepole required to be impregnated with the preservative.

In practice, I have found it necessary, in order to effect good results,to immerse the poles to a depth about one-fifth greater than the lengthof that part of the pole which it is desired to impregnate. A polethirty feet long, say, and required to be impregnated at its butt for adistance of six and one-half feet should. have the butt immersed aboutfrom seven and one-half to seven and threefourths feet.

After the air and moisture have been sufficiently expelled or extracted,which requires. about six hours immersion for the average run of airseasoned timber, I continue to maintain the temperature of thepreservative as nearly stationary as possible 235 F. to 240 F.) and thenproceed to raW off the preservative liquid slowly from the treating tankthus gradually exposing the upper part of the submerged portion of thepole to atmospherictemperature, whereby the rarefied vapors and air inthe cavities of the wood begin tocontract and form a partial vacuumwithin thepole which causes the preservativeliquid to rise through thebottom of the pole. The preservative is gradually drawn off from thetreating tank and the pole gradually cools from the upper point of thesubmersion downward so that the bottoms of the poles are all the whilesealed against the entrance of air throughout the treating process andthus no cold liquid reaches the bottom of the poles, whereby viscosityof the liquid is not so raised as to clog or seal the pores.

The advantage of gradually drawing off the liquid while thetemperatureof the liquid is held at an elevated degree of heat isthreefold. (1) The viscosity of the preservative liquid is, kept in themost favorable condition for easy penetration through the cavities ofthe wood fiber. (2) At no time can air enter and take the place of thepenetration of the preservative since the butts of the poles are sealedby hot preservative to the end of the impregnating period of the poles.(3) The vacuum is formed gradually in the wood,

from the upper point to which the poles have been submerged, downward tothe bottom as the hot preservative is slowly drawn from the treatingtank. This mode of creating the vacuum gives a uniformity of action tothe forces distributing the liquid and also lends time for more evenpenetration through the more minute capillary voids in the Wood.

In other words, the conditions are such that (1) Heating thepreservative liquid" to a temperature that will exclude absorption ofthe liquid by the poles when first immersed in the liquid, for thereason that the gases and moisture in thewood will be expanded withsufficient force to prevent the preservative from entering the capillarycavities'in the wood.

(2) The preservative is kept at a stationary or constantly risingtemperature during the period of driving out the air and moisture,-sothat little or no absorption of the liquid takes place in the polesduring this initial period of the treating process. (3) The poles areheated to a greater depth than the space required to be treated, inorder to obtain a more perfect expulsion of air and moisture therebyproducing a better vacuum out the impregnating period'so that there isno chance for air to enter the wood and interfere with the treatingprocess while it is in operation.

From the foregoing description it will be .seen that the timber is in noway injured, that .no holes are formed therein seeking to allow the.impregnating material to pass into the body of. the wood, andfurthermore, no large 'Itwill, of course, be appreciated that in sofaras. the generic invention is concerned {vats or receivers arenecessary to carry out 'my-process'. 4 :It Wlll alsobe seen that nopressure, other than atmospheric pressure, is employed in carrying-outthe process, hence no expensive apparatus is needful;

that instead of lowering the preservative in the tank or vat-in whichthe pole or timber isplaced, that the pole or timber may be graduallyraised and thus the same effect produced as if the level of the liquidwere gradually lowered. The claims, therefore,

where they employ the phrase securing a relative and gradual withdrawalof thebath with reference to the'timber are to be so interpreted as tocover either the lowering of the level of the bath or the gradualraising'of thetimber out of the bath.

Various forms of apparatus may be employed for carrying out the methodvabove set forth but it is, not deemed essential to an understanding ofthe invention to illustrate the same.

What is claimed is:

1. The process of impregnating timber which consists in immersing thesame, in

part atleast, in E bath of liquid impregnating material'ralsed to atemperature sufliciently high to cause such an expanslon of the vaporsand moisture content of the' timber as to preclude the entrance of theimpregnating material into the timber;

maintaining the temperature of the bath;

and finally securing a relatii e and gradual withdrawal of the bath withreference to the timber.

2. The process of impregnating timber which consists in immersing thesame in a bath of liquid impregnating material raised 3. The process ofimpregnating the butt;

of a'pole which consists in immersing the butt in a bath of impregnatingliquid maintained at a high temperature; allowing the butt to remain inthe liquid for an appreciable time interval; and finally graduallywithdrawing the bath from the butt while still. maintaining the bath ata high temperature.

4. The process of impregnating the butt of a pole which consists inimmersing the butt in a bath of hot liquid impregnating material, thedepth of immersion being some what in excess of the extent to whichimpregnation is desired in the butt; retaining the hot liquid about thebutt for an appreciable time interval; and finally gradually loweringthe bath about the pole.

5. The process of impregnating the butt of a pole which consists inheating the butt by immersing it in a bath of heated impregnatingmaterial and thereby producing a partial vacuum in the cavities andpores in the butt by the expansion and expulsion of the contained gasesand moisture content;

' pregnating material into the butt.

In testimony whereof I have signed my name to this specification.

'THEODORE W. SMITH.

